A conventional gas laser oscillator is known in Patent Literature 1, for example. In the gas laser oscillator disclosed in Patent Literature 1, a high voltage is applied between two electrodes disposed in a discharge tube, and thereby a discharge space is generated in the discharge tube. Laser gas is excited by the discharge space and output to the outside as a laser beam through the total reflection mirror and the partial reflection mirror that are disposed at the respective ends of the discharge tube. A gas circulation path that forms the circulation path of the laser gas is connected to the discharge tube, and a blower is disposed inside the gas circulation path. This blower allows the laser gas to circulate in the discharge tube and the gas circulation path.
In the gas circulation path, the blower includes a rotor chamber that incorporates a rotor for blowing gas. The blower also includes a gear chamber that incorporates gears for determining the rotation timing of the rotor. The blower also includes a driver for driving the gears. The rotor and the driver are connected to each other by a shaft. The rotor chamber is connected to the gas circulation path and the rotor allows the laser gas to flow. The pressure of the laser gas is monitored by a gas pressure detector such that the pressure inside the gas circulation path is kept constant.
On the other hand, in the driver of the blower, the rotation of a motor, for example, transmits the motive power to the rotor in the rotor chamber. Lubricating oil is housed in the gear chamber so as to lubricate the bearings and the gears. In order to suppress the entry of the oil mist generated from the lubricating oil into the laser gas circulation path, a seal part is disposed between the rotor chamber and the gear chamber and separates the rotor chamber and the gear chamber. However, a small gap is present between the seal part and the shaft for connecting the rotor and the driver. In order to prevent the entry of the oil mist from the gear chamber to the rotor chamber through this gap caused by vacuum diffusion, the pressure of the gear chamber is set lower than that of the rotor chamber. In this manner, the structure of the technique disclosed in Patent Literature 1 prevents the entry of the oil mist into the gas circulation path when the pressure in the gear chamber varies in acceleration and deceleration of the operation of the blower.
However, when the gap between the seal part and the shaft is increased by abrasion or age deterioration, even in steady operation, the pressure difference between the rotor chamber and the gear chamber is decreased and the pressure difference for preventing the entry of the oil mist cannot be obtained in some cases.
Thus, the continuous operation in this state can cause the entry of the oil mist generated in the gear chamber into the gas circulation path, and thereby decreases the output of the laser beams.
As a measure against the decrease in the pressure difference between the rotor chamber and the gear chamber, an alarm part issues an alarm when the gear chamber pressure detector connected to the gear chamber detects that the pressure of the gear chamber is equal to or higher than a predetermined pressure.
However, when the predetermined pressure is excessively high, a decrease in the pressure difference between the rotor chamber and the gear chamber cannot be detected properly and the output decreases. Conversely, when the predetermined pressure is excessively low, the alarm is frequently issued within a short period of time, which shortens the maintenance interval and increases the running cost.